1. Field of the Invention
Certain embodiments of the present invention relate to arc welding. More particularly, certain embodiments of the present invention relate to systems and methods for providing controlled AC arc welding processes, and in particular AC TIG welding processes.
2. Description of the Related Art
Certain prior art welding systems use bridge topologies in a welding power source to provide AC welding capability. A half-bridge topology may be used in a welding power source having dual output current paths configured to share a common path, such that each output can induce a flow of opposite polarity in the shared path. In practice, many welding power sources are configured as such and may require only the addition of a second set of rectifier devices to complete the second path. A switch may be placed in the non-shared path of each power source leg and the direction of current flow through a connected welding output circuit path is determined by the active leg. A full bridge topology may be used with just about any power source topology, providing flexibility and the potential to be added to existing designed power sources. The full bridge topology allows easy implementation of zero cross assisting circuits. A blocking diode may be used to protect the devices in the power source from high voltage transients that occur during the zero cross.
For certain short circuit transfer welding processes such as, for example, a surface tension transfer process, the output current must decay rapidly to specific values at certain points in the process. Techniques have been applied in the prior art to achieve such rapid reductions in output current in DC positive and DC negative applications. However, the ability to rapidly reduce the output current in both positive and negative directions in an AC arc welding process, while keeping leakage currents and spatter to a minimum and while allowing an arc to easily re-establish between a consumable electrode and a workpiece after the transfer of a molten metal ball from the electrode to the workpiece, is a challenging problem. This is especially true in TIG (tungsten-inert-gas) welding operations, where peak current and frequency limitations are encountered.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems and methods with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.